The table in the Mexican beach bar was full. There wasn't an inch left uncovered by colorful maps, which were held down by two empty Sol beer bottles and a frosty full one.

"You should go to Tulum," he said, barely audible above the thumping house music. "The Mayan ruins are on a cliff by the water."

But I wasn't interested in scrambling up Mayan stairways with the gringo throngs. While the stone memories of the Maya are scattered throughout the Yucatan Peninsula and lure millions of visitors each year - especially now with the widely misunderstood end of the Mayan calendar looming in December - the ruins are merely the showiest element of the ancient culture.

I was in the Yucatan, in the southern fringes of the busy Riviera Maya resort region, to find a place where learning about the Maya is more authentic, more natural, more immersive. To see the land the way they did then, instead of the way tourists do now.

The preserved natural areas here might not have been home to bustling cities, but figured just as importantly in Mayan culture - sites integral to daily living and religion. There are no shelves full of stone carvings or racks of "I (heart) Cancun" key chains in the gift shop. Buses full of visitors and attraction lines are conspicuously absent.

"I'm going to Sian Ka'an," I said. I set my full bottle down on a map with an oversized patch of green south of Tulum.

The waiter silently cleared my empty bottles, then leaned over to tell me something - probably that I'd squandered a chance to see one of the top five tourist attractions in the area, I figured.

"That's my favorite," he said. "Almost nobody goes there."

Where sky is born

In Mayan, the name Sian Ka'an translates to "where the sky is born" - and standing at the edge of one of the vast lagoons at the edge of the Caribbean, it can seem that there is nothing but sky, emerging from the waves.

At 2.3 million acres, the Sian Ka'an Biosphere Reserve is the largest protected area in the Mexican Caribbean. The northernmost part of the reserve contains what is thought to be an ancient trade route through lagoons and mangrove channels between the cities of Tulum and Muyil about 15 miles south.

At Muyil, a place where only about 45 people visit daily, my guide and I walked among crumbling Mayan temples. The largest of which, the Castillo, is topped by a circular tower - once used as a lighthouse. Its windows and thatched roof gave it the appearance of a large monster staring out to sea, perhaps intentionally constructed to scare potential intruders.

From Muyil, we slid kayaks into the water and paddled to the edge of Chunyaxche, a brilliant turquoise lagoon linked to the open sea by a narrow canal system dredged by the ancient Maya to provide access to the Caribbean. We could have made the trip in small boats with noisy outboard motors, but the kayaks were closer to the Maya's wooden dugouts.

On the far side of the lagoon is a small building that was used as a Mayan customs post on the route where salt, chicle (gum), honey, and incense were once traded.

Here, between the lagoons in a freshwater canal edged with mangroves, we slipped out of the kayaks, jumped into the water and floated along with the current for nearly an hour. Tiny fish surrounded us, but scattered quickly when I reached toward them.

From this angle especially, it was easy to see what they saw - in nature and in belief. Birthplace of the sky, indeed.

The cenote bird

The wide-open spaces of this largely flat region continue underground in cenotes, the deep limestone sinkholes scattered throughout the peninsula. The fresh-water pits, called dzonot in Mayan, served as the main source of water for the ancient civilization, as well as portals to dark places.

Xibalba, the Mayan underworld, is described in creation stories as the parallel unseen "Otherworld." It was a place of fear where the dead had to traverse an obstacle course of bats, jaguars, rivers of blood and rooms of sharp knives. Caves and cenotes were the gateways to this aqueous, hellish underworld.

The artificial illumination in Aktun Chen, a huge dry cave and cenote system near Akumal, made the idea of Xibalba seem much less threatening. The deep, crystal-clear water made it easy to see the white floors of the natural wells.

In this surreal world of stalactites, stalagmites, fossils and bats beneath the curling thick ocean of emerald jungle, the still cenote water became a mirror for the fantastical rock formations.

Ahead of me, in the sunlight shining through a hole in the cave ceiling, a motmot perched on a stalagmite. The colorful bird with a distinctive blue racket-shaped tail can nearly always be found near cenotes, and is considered an emblem of these water features.

"The Maya say that the motmot used to be the most beautiful bird in the jungle, but he was proud," said my guide. "After a hurricane, he lost some of the feathers in his tail and was so embarrassed, he hid near cenotes."

I tiptoed slowly through the cavern, hoping to get closer to the motmot, when a second bird landed on a nearby rock outcropping. The two birds called to each other with the mot-mot sound that gave the bird its name. As I inched closer, they suddenly launched and flew through the open ceiling, into the dense jungle.

On the floor of the cave was a bright blue feather - the rounded end of one of the tail feathers. They're considered good luck, and a sign that you'll return to the Mayan world. I held it gently in my fingers until we were outside, then tucked it into my pocket, next to the map of Sian Ka'an.

Path to Xibalba

On my map, now overly creased and softened by wear, small dots showing cenotes in the region appeared as small constellations. Today, many are open to the public for swimming, snorkeling and diving.

In the thick jungle south of Akumal, I walked from the parking lot with my dive guide toward the gaping limestone maw of the Dos Ojos ("two eyes") cenote. The screeches of children playing near the cave entrance bounced off the undulating stone and through the trees. At the opening, the sunlight on the shallow, sandy bottom caused the water to glow turquoise.

I sat on a small, wooden stairway that disappeared into the liquid, tied my flashlight onto my wrist and slipped beneath the surface. The silence in this underwater cavern was different from the sound of diving or snorkeling in the Caribbean, where there's a constant clatter of fish. All I could hear were the bubbles that signaled my breathing.

The beam of my flashlight served as a spotlight on stalactites and stalagmites, fossils and tiny fish. Glowing through the water far ahead was such a serene shade of blue that I found myself holding my breath. Below me were huge fissures in the limestone that made me wonder about the Mayan view of the underworld. If Xibalba is a hellish place, the pathway there seemed quite the opposite. Was the idea to calm the dead, to prepare them for what's ahead?

At the end of our dive, I spent some time alone at the gateway to Xibalba. The children from earlier were gone. I floated in the luminous water, enjoying the stillness and surroundings - probably much of it unchanged since the Mayans lived, worked and worshiped here.

It was a moment not in the resort brochures or in the guide books, but was perhaps closest thing I'd found to a kernel of Mayan time. Some moments are best found on maps - in places where "almost nobody goes."

Calling Sian Ka'an Biosphere Reserve home

1.3 million acres

375 species of bird

115 species of mammals

90 species of native bees

47 species of dragonflies

74 species of beetles

276 species of crustaceans

310 species of mosquitoes

318 species of butterflies

84 species of coral

1,048 species of flora

If you go

Getting There

Cancun International Airport (CUN) is the gateway airport to the Riviera Maya. The southern region - including Akumal, Tulum and the Sian Ka'an Biosphere - is about two hours south of Cancun. Some hotels provide airport transfers, although if you're planning to explore the area, arrange for a rental car or a driver.

Community Tours Sian Ka'an: 134 Avenida Tulum, between Escorpion and Libra Sur, Tulum; +52 (984) 871-2202; www.siankaantours.org. A Mayan ecotourism organization, this group leads history and adventure tours in the Sian Ka'an Biosphere Reserve, from kayaking to birding to visiting the Muyil archaeological site. Kayak tours are $45 per person.